This invention relates to a process for the production of delayed action tin catalysts. These delayed action tin catalysts are suitable for catalyzing the reaction between isocyanate groups and isocyanate-reactive groups in a process of making a polyurethane.
Many polyurethane applications use catalysts which are heat activated so that mixtures of the co-reactants have long potlives at room temperature, but react almost immediately when heated to a temperature above the catalyst activation temperature. Current state-of-the-art delayed action catalysts include nickel catalysts, mercury catalysts, bismuth catalysts, and amine catalysts blocked with carboxylic acids. Each of these groups of catalysts has disadvantages associated with their use. Nickel catalysts are used in relatively high levels (i.e. 0.5 to 3.0% by weight, based on the polyol weight). Mercury based catalysts are poisonous and, thus, serious health risks are associated with their use. Catalysts based on bismuth are water sensitive and deactivate in the presence of moisture. Accordingly, these catalysts are not suitable for any application in which water is present or added. The acid-blocked amine catalysts have an unpleasant odor associated with their use. This unpleasant odor remains in the final product, making these catalysts unsuitable for some applications.
Other known delayed action catalysts include various tin-sulfur catalysts such as, for example, tin mercaptoacetates, tin mercaptides and tin sulfides. Of these, the tin mercaptoacetates are known to be sensitive to both acids and to water, which limits their usefulness to application areas which are free from acids and water. The tin mercaptides show some delayed action, but the activation temperature is too low to be of much use commercially. Both the tin mercaptoacetates and the tin mercaptides are more reactive at room temperature than is typically desirable for a delayed action catalyst. Finally, the tin-sulfides have an unpleasant odor associated with their use. The unpleasant odor of these catalysts make these unpopular delayed action catalysts also.
U.S. Pat. No. 3,813,424 discloses a process for the manufacture of dialkyltin oxide. This process comprises alkyl iodide directly with metallic tin to form dialkyltin iodide, followed by hydrolysis to the form the corresponding dialkyltin oxide. Dialkyltin oxides are effective urethane catalysts, but do not have the delayed action feature desired in many applications.
Light stable elastomers and a process for their production are disclosed by U.S. Pat. No. 5,714,562. These elastomers comprise the reaction product of an isocyanate prepolymer, a chain extender and a catalyst selected from i) solid delayed action catalysts having a melting point of greater than about 60.degree. C., ii) alkyl substituted organotin catalysts containing alkylmercaptide ligands which are liquid at room temperature, and iii) alkyl substituted organotin catalysts containing sulfur bridging groups which are liquid at room temperature. Light stable elastomers are based on aliphatic diisocyanates, the reactivity profile of which is quite different from the more widely used aromatic polyisocyanates. Due to the much lower reactivity of aliphatic vs. aromatic isocyanates, it is much easier to make heat activated systems based on aliphatic isocyanates.
Various organotin catalyst compositions are disclosed in U.S. Pat. No. 5,646,195. U.S. Pat. No. 5,646,195 describes delayed action dialkyltin sulfide catalysts that are useful in carpet backing applications. The delay in gellation provides improved handling and backing quality.